Copyright is owned by the Author of the thesis. Permission is given for a copy to be downloaded by an individual for the purpose of research and private study only. The thesis may not be reproduced elsewhere without the permission of the Author.

Institute of Food Nutrition and Human Health College of Sciences,

A Field Investigation into the Relationship

between LA90 and LAeq Sound Level Descriptors in New Zealand

A thesis presented in part fulfilment of the requirements for the degree of Master of Philosophy [Science] Majoring in Environmental Acoustics at Massey University Wellington New Zealand

Lindsay John Hannah

December 2011

i

ii

Certificate of Originality

I Lindsay John Hannah hereby state tthat this submission is my own work and that, to the best of my knowledge, understanding and belief, it contains no material previously published or written by another person, except where due reference, credit and full acknowledgement is made in the body of the text.

‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ Lindsay Hannah. December 2011

iii Reproduction of Work [in Part or Full]

Information presented in this thesis and body of work [including the appendices] is commercially sensitive and has been provided to the author on the basis that this thesis in its entirety and all related field work shall not be reproduced in any manner including electronically or physically, in part or full, without the acknowledgement and express written permission of Lindsay John Hannah.

iv

Thesis Dedication

This thesis is foremost dedicated to my family, especially my late mother Elizabeth, surrogate mother Katrine, beautiful wife Michaela and daughter Sophie Elizabeth. I would also like to dedicate this thesis to my sister Alison and niece Aerin Elizabeth.

I also dedicate this thesis to everyone who has helped me with my academic studies and acoustic consulting career so far, including those mentioned beneath in the acknowledgements.

v

vi

Abstract

Wind turbine generator acoustics is an issue for communities as it is people within these communities that occupy dwellings. The current New Zealand wind turbine standard NZS6808:2010 Acoustics – Noise, places priority on received sound pressure levels at dwellings remote from the wind turbine rather than from sound emission at the wind turbine generator itself.

As part of assessment under NZS6808:2010, background noise levels are required to be measured [as LA90] at selected relevant receiving locations off site before a wind farm site can be developed. Allowable sound limits are then derived [as LAeq] from a comparison of the predicted wind turbine sound pressure levels and the actual measured average background noise at the nominated off site receiving location[s].

A disparity arises with the use of two different sound level descriptors used for assessment under the standard, namely the statistical LA90 versus the LAeq energy average sound level descriptors. In order to account for the possible variation between the LA90 and LAeq sound level descriptors NZS6808:2010 requires LAeq predicted sound pressure levels to be

‘converted’ to received LA90 sound pressure levels as part of the acoustic prediction process and hence NZS6808:2010 states the predicted LAeq sound pressure levels at any receiver location are to be treated as equivalent to the LA90 value.

At the time of commencing this study the [then] current New Zealand wind turbine standard NZS6808:1998 Acoustics – The Assessment and Measurement of Sound from Wind Turbine Generators stated that background noise levels were ‘typically 1.5 dB to 2.5 dB’ lower than the predicted LAeq sound pressure levels for wind turbine generator sound.

Unlike the current standard, NZS6808:1998 did not provide any means to account for the disparity between the background noise levels and predicted wind farm sound levels as part of the wind farm assessment process. A key implication being that under NZS6808:1998 wind turbine sound could potentially exceed the allowable 40 dBA design sound limit [or average background noise level + 5 dB] by up to a further 2.5 dB and still remain in compliance with the limits recommended under the NZS6808:1998.

The impetus and motivation behind this study has consequently been to endeavour to quantify the variability between wind turbine generator sound descriptors [LAeq and LA90] both on the wind farm site and at a remote receiver dwelling location where people actually reside.

The research outcome is relevant as at the time of commencing this thesis NZS6808:1998 was being reviewed by experts and practitioners in the area of wind turbine acoustics. This review included assessing any differences in sound level descriptors.

vii

This review provided the incentive for the thesis being particularly valuable, unique and practical so far as any actual measured field results were relative to wind turbine generators in New Zealand and the New Zealand Standards operating environment.

In order to carry out the evaluation between LAeq and LA90 sound level descriptors an assessment based around a semi‐empirical field study of objective field measurements and subjective observations was conducted at two wind farms in the lower North Island of New Zealand. The study assessed present day, commercial class, horizontal, three bladed wind turbine generators located over heterogeneous terrain.

The principal implication of the study related to the collection of uncontaminated wind turbine sound level samples. A raw data set of 11,150 [10 minute LAeq/LA90 sound level samples] were collected over a 12 month period. From the total sample, merely 39 [or less than 2% of the total raw sample] were actual uncontaminated wind turbine sound samples only.

The conclusion here is that due to the high number of intervening variables it is a challenge to collect a large sample set of uncontaminated wind turbine sound data. Based on the data collected, it could potentially take several years to collect a suitable uncontaminated sample of say 1,500 [10 minute samples] from wind turbine sound only at remote locations off the wind farm site using such methods. Data collection and analysis was not an issue on the wind farm site itself due to the measurement location and wind turbine being in close proximity.

The results of the field study illustrated that based on the final data set of 10 minutes sound level sampling [n=39] the overall mean sound level difference [LAeq ‐ LA90] for wind turbine sound was 2.4 dB at a remote residential location some 1200m from the wind farm site. The overall mean sound level difference for wind turbine sound levels based on the wind farm was 1.4 dB [at the nominated Ro location].

As a result of the study’s findings it is concluded that although the field data indicated a quantifiable level difference between the two sound level descriptors the current wind turbine noise standard [NZS6808:2010] rightly removes any uncertainties by stating that

LAeq = LA90 when carrying out the assessment process.

Therefore the removal of any uncertainty is chiefly due to the fact that although a quantifiable level difference between the two sound level descriptors was achieved for this study the sound level difference is prone to change and any precise or exact level difference is therefore a factor of the wind turbine generator models tested site conditions and related intervening variables.

viii

Acknowledgements

Mr Malcolm Hunt. Director and Principal, Malcolm Hunt Associates Noise and Environmental Engineers. I would like to thank Malcolm for allowing me the opportunity to complete further tertiary study. As Malcolm was on the committee for all wind turbine acoustic standards in New Zealand I would also like to thank him for assisting me with the original concept for the study. I would also like to thank Malcolm for mentoring me with university work and my consulting work in the field of acoustics. I am eternally grateful for his support over the last eleven years as an expert in the field of environmental acoustics and the support he has provided my family and I during this time as my director.

Mr Miklin Halstead. Senior Associate, Marshall Day Acoustics Limited. I would like to thank Miklin for assisting me with this study in particular assistance with work relating to field equipment such as the audio field recording and taking the time to provide comment and discuss concepts around the work.

Dr Stuart McLaren ‐ Senior Lecturer in Health Sciences and Dr Wyatt Page ‐ Associate Professor of Acoustics and Human Health, Institute of Food Nutrition and Human Health, College of Science, Massey University [Wellington Campus].

I would like to thank both Stuart and Wyatt for their professional assistance with this work and always making themselves available to discuss the thesis. I would especially like to make mention of the support given by Stuart in terms of his holistic approach to study in terms of my consulting work, study and all important family. I would also like to thank Wyatt who came into the lead supervisor role at a very significant time and provided me with both support and guidance in the critical end stages of the thesis. Without Stuart’s and Wyatt’s assistance I would not have been able to complete the work to the high standard it is. I have learnt a great deal from the meetings I have had with both Stuart and Wyatt. Finally, I am eternally grateful for the long term support provided by Stuart and Wyatt while completing the thesis with a young family on a part time basis.

Mr Paul Botha. Wind Development Manager, . I would like to thank Paul for assisting me with sourcing the required background information regarding the all important wind data for the study sites. As Paul was on the most recent wind turbine acoustic standards committee I would like to thank Paul for taking the time to meet with me and discuss questions I had relating to the wind farm sites and the latest standard process. Without the support of Paul I would not have been able to carry out the study at the two selected sites and for this I am eternally grateful.

ix

I would like to thank Alison Mann and Michaela Hannah for the very long periods of time spent in review and comment on the final body of work. I would like to make special mention of my wife, Michaela, who without her support I would not have been able to make literally dozens of return trips at all times of the day and night to and Makara to carry out the required field work.

I would like to say thank you to all the Meridian Energy and staff at the wind farm sites who helped me with the onsite logistics and allowed me to undertake onsite measurements. There are too many individuals to show individual appreciation but all were so kind and willing to help me.

I would also like to make special thanks to the occupants of 403 Makara Road who without their kind permission I could not have conducted many hours of measurements at their site.

x

Table of Contents Certificate of Originality ...... iii Reproduction of Work [in Part or Full] ...... iv Thesis Dedication ...... v Abstract ...... vii Acknowledgements ...... ix Table of Contents...... xi List of Figures ...... xv List of Tables ...... xxi Chapter 1: Introduction and Purpose of the Study ...... 1 Introduction ...... 1 Structure of Thesis ...... 5 Chapter 1: Introduction and Purpose of Study ...... 5 Chapter 2: Wind Turbine Generator Terms and Conventions ...... 5 Chapter 3: Acoustic Terms and Conventions ...... 5

Chapter 4: LA90 and LAeq Sound Level Descriptors in Wind Turbine Acoustics ‐ A Literature Review ...... 5 Chapter 5: Generation ...... 5 Chapter 6: Aero Acoustics – Wind Turbine Generator Acoustics ...... 6

Chapter 7: A Field Investigation into the Relationship Between LA90 and LAeq Wind Turbine Sound Level Descriptors in New Zealand ...... 6 Chapter 8: Discussion ...... 7 Chapter 2: Wind Turbine Generator Terms and Conventions...... 9 Introduction ...... 9 The Anatomy of a Wind Turbine Generator ...... 9 Wind Turbine Components and Concepts ...... 14 Chapter 3: Acoustic Terms ...... 19 Introduction ...... 19 Objective and Subjective Acoustics ‐ Noise and Sound ...... 19 Acoustic Concepts ...... 19

Chapter 4: LA90 and LAeq Sound Level Descriptors in Wind Turbine Acoustics – A Literature Review ...... 39 Introduction ...... 39

Wind Turbine LA90 and LAeq Sound Level Descriptor Studies ...... 40 Research of G.P Van den Berg ...... 41 Ramakrishnan Review ...... 44 New Zealand Studies and Reviews ...... 46 Wind Turbine Sound Sources ...... 48 Aerodynamic Sound from Wind Turbine Generators ...... 52 Navier Stokes Equations ...... 65 Lighthill Theory ...... 65 Low Frequency Sound and Infrasound ...... 66

xi

Annoyance from Wind Turbine Generator Sound ...... 68 Low Frequency Sound and Health Effects from Wind Turbine Generators ...... 69 Vibro‐Acoustic Disease [VAD] ...... 73 Wind Turbine Syndrome ...... 75 Impacts of Low Frequency Sound Perceptions and Investigations ...... 75 Tonal Sound for Wind Turbine Generators ...... 76 Impulsiveness of Wind Turbine Generator Sound ...... 76 General Spectrum of Wind Turbine Generator Sound ...... 77 Vibration ...... 79 Seismic Monitoring ...... 80 Wind Turbine Generator Acoustic Standards ...... 80 International Standard IEC 61400‐11: Wind Turbine Generator Systems Part 11: Acoustic Noise Measurement Techniques ‐ Wind Turbine Sound Power Measurement Standards...... 80 NZS6808:1998, Acoustics – The Assessment and Measurement of Sound from Wind Turbine Generators and NZS6808:2010 Acoustics Wind Farm Noise ...... 81 Evaluation of NZS6808:2010 Noise Limits versus Noise Limits in Other Countries ...... 83 Chapter 5: Wind Power Generation ...... 85 Introduction ...... 85 Fundamentals of Wind Power Generation ...... 86 The World Wide Development and Evolution of Wind Energy ...... 86 Limits on the Wind Capacity ...... 90 Chapter 6: Aeroacoustics – Wind Turbine Generator Aerodynamics ...... 93 Introduction ...... 93 Rotor and Blade Aerodynamics ...... 93

Chapter 7: A Field Investigation into the Relationship between LA90 and LAeq Wind Turbine Sound Level Descriptors in New Zealand ...... 97 Introduction and Overview ...... 97 Structure of Study ...... 99 Background Information ...... 99 Verbal Description of Test Sites ...... 99 Geographic Location and Mapping of Test Sites ...... 100 Wind Turbine Generator Locations ...... 101 Position of Selected Test Turbines and Sound Assessment Locations ...... 104 Photo of Test Sites and Wind Turbine Generators ...... 109 Description of Test Wind Turbine Generators ...... 113 Technical Specifications of Test Wind Turbine Generators ...... 114 Technical Drawings of Test Wind Turbine Generators ...... 115

Test Wind Turbine Generator Sound Power Level [Lwa] ...... 116 Assumed Turbine Sound Power Level ...... 117 Measurement Equipment ...... 119 Calibration and Specifications of Measuring Equipment used in Study ...... 123 Surrounding Environments of Wind Farm Test Sites ...... 124 Wind and Climatic Conditions for Test Sites ...... 129

xii

Method of Investigation ...... 134 [Makara] Wind Farm ...... 135 ...... 141 Data Filtering and Additional Limitations for Field Work ...... 142 Data Filtering Project West Wind [Makara] Wind Farm [Data Logger] ...... 147

Data Filtering Te Apiti Wind Farm Ro Measurement Location [Data Logger] ...... 156

Additional Te Apiti Wind Farm [Handheld Measurements at Ro & Base of Turbine] ... 159 Method of Data Analysis ...... 161 Results ...... 166 Descriptive Statistical Summary of Results and Observations ...... 175 General Observations...... 175 403 Makara Road – Project West Wind [Makara Wind Farm]...... 176 Te Apiti Wind Farm ...... 183 Chapter 8: Discussion ...... 185 Introduction ...... 185 Synopsis of Final Results [Data Set N – 403 Makara Road] ...... 185

Synopsis of Final Results [Ro Measurement Position] ...... 185 Summary Statement of Final Results ...... 186 Background to Study ...... 187 The Studies Individuality, Innovation and Contribution to Wind Turbine Acoustics in New Zealand ...... 190 A Semi‐Empirical Study ...... 192

Relationship between LA90 and LAeq Sound Level Descriptors ...... 192 Variability of Results ...... 194 Accuracy of Measurement Results ...... 195 Spearman’s and Kendall’s Rank Correlation Coefficients – A Measure of Association

between LA90 and LAeq ...... 196 Kendall’s Rank Correlation Coefficient ...... 198 Spearman’s Rank Correlation Coefficient ...... 199 Statistical Significance using Spearman’s & Kendall’s Rank Correlation Coefficients... 202 Data Sample Size ...... 202 Variability and Data Spread in Results as a Function of Wind Turbine Generator Design, Surrounding Environment and Operating Mode ...... 203

Comparison and Analysis of Sound Level Descriptors [LA90 and LAeq] ...... 209 Comparison and Analysis of Sound Level Meter Measurement Time Weighting and Sample Interval ...... 215

Comparison of Sound Level Meter Signal Processing for LA90 & LAeq Sound Level Descriptors ...... 216 Mechanisms and Intervening Variables Relating to Measured Results ...... 219 Measurement Uncertainty ...... 219 Recommendations and Further Work ...... 223 Major Assumptions and Limitations to Body of Work ...... 225

xiii

Appendix A ...... A.1 Introduction ...... A.1 Sources of Wind ...... A.1 Wind Scales ...... A.4 Wind Turbine Generator Available Wind Power ...... A.5 Power Density Function ...... A.6 Wind Shear and the Increase of Wind Speed with Height ...... A.7 Wind Speed and Energy Variation with Elevation ...... A.9 Roughness Classes and Roughness Lengths ...... A.10 Topographic Effects on Wind Speeds ...... A.10 Modelled Wind Speed ...... A.15 Wind Direction ...... A.16 Wind Speed ...... A.17 New Zealand Wind Capacity...... A.17 Aerodynamic Power Control in Wind Turbines Generators...... A.18 Stall ...... A.20 Pitch ...... A.22 Yaw ...... A.22 Mechanical Power Extracted from Wind ...... A.23 The Power Co‐efficient ...... A.24 Wind Energy Power Output Based on Wind Speed ...... A.25 Wind Speed versus Power Output ...... A.28 Sound Power Curve – Wind Speed, Power Output and Sound Power Levels ...... A.29 Approximate Calculation of Energy Yield from the Wind ...... A.30 ...... A.30 Feasible Power Rating ...... A.31 References ...... A.31 Appendix B ...... B.1 Introduction ...... B.1 Aerodynamic Lift [Force] ...... B.1 Torque 2 Betz’s Elementary Momentum Theory [Disk Actuator Theory] ...... B.5 Rotor Blade Geometry ...... B.7 Shape ...... B.7 Number of Rotor Blades ...... B.8 Two‐Bladed [Teetering] Concept ...... B.10 Optimum Rotor Blade Shape ...... B.11 Blade Tip Aerodynamics ...... B.14 Rotor Blade [Tip] Designs ...... B.15 Tip Speed Ratio ...... B.16 Tower Aerodynamics ...... B.18 Downwind Wind Turbines Generators ...... B.20 References ...... B.22

xiv

List of Figures Figure 1: Front and side elevation of a three bladed horizontal wind turbine ...... 10 Figure 2: Simple configuration of a Horizontal wind turbine generator...... 11 Figure 3: Photo of modern commercial three bladed horizontal wind turbine generator...... 12 Figure 4: Modern commercial three bladed horizontal wind turbine generator...... 13 Figure 5: Mechanical drive system of a wind turbine ...... 14 Figure 6: Common wind turbine generator technologies ...... 17 Figure 7: Conceptual diagram of the mechanical‐electrical function chain in a wind turbine. .. 17 Figure 8: Overview of the electricity generation, transmission and distribution ...... 18 Figure 9: Propagation of a sound wave...... 21 Figure 10: Displacement & pressure variation of a pure sound wave [sinusoidal pressure] . .... 22 Figure 11: Octave band based on centre frequency band widths...... 26 Figure 12: Third octave band based on centre frequency and widths...... 26 Figure 13: Factors moderating potential noise annoyance ...... 27 Figure 14: Schematic of human ear and sound paths...... 28 Figure 15: Basic structure of the human ear...... 29 Figure 16: Example of threshold of hearing [audibility] for 18 to 25 year old age range ...... 30 Figure 17: Example of various time varying acoustical sound level descriptors...... 34 Figure 18: A representation of the radiation of sound from a simple source in free field ...... 35 Figure 19: Correction for air attenuation including the inverse square law ...... 36 Figure 20: Approximation of sound fields ...... 37 Figure 21: Location of wind turbines and measurement location [A] for Rhede wind farm near the Dutch/German border ...... 42

Figure 22: Comparison of 48 hour sound measurements levels [LAeq and LA95]. Measurements presented at 5 min intervals at measurement location A [400m from wind farm]‐ turbines are considered the dominant sound source from site observations...... 43 Figure 23: Comparison of turbine noise statistics ...... 47 Figure 24: Components and total sound power level of a 2MW wind turbine, showing structure‐borne [s/b] and airborne [a/b] transmission paths ...... 49 Figure 25: Sample of time varying wind turbine generator [under load] of a modern 3 MW wind turbine [measured at base approx 2 m from generator inside steel tubular base of tower with door closed ...... 50 Figure 26: Acoustic photograph showing the high speed tips of a wind turbine ...... 55 Figure 27: Sectional elevation through of a typical wind turbine rotor blade and key components. Two dimension sectional view...... 56 Figure 28: Flow around a wind turbine rotor blade – three dimension view...... 56 Figure 29: Six mechanisms of aero‐acoustic sound ...... 57 Figure 30: Rotor with trailing‐edge serrations, including noise sources on rotating blades...... 60 Figure 31: Blade tip shape influence on wind turbine sound radiation ...... 62

xv

Figure 32: Distribution of instantaneous values of Powell’s sound source ...... 63 Figure 33: [left] Spectrogram of sound pressure levels measured near a GE 1.5 MW wind turbine generator. [Right]: Spectrogram of sound pressure levels measured near a Vestas 1.8 MW wind turbine generator ...... 64 Figure 34: ISO 7196: 1995 Acoustics – Frequency Weighting Characteristic for Infrasound Measurements G weighting scales ...... 70 Figure 35: Perception threshold of human ear ...... 71 Figure 36: External sound pressure level versus 85 dBG threshold...... 72 Figure 37: Frequency distributions within the 1.6 – 500 Hz range, of the A340 cockpit in cruise flight and of a commuter train ...... 74 Figure 38: Low frequency sound from a wind turbine. 1/24 octave band analysis ...... 77 Figure 39: Vestas V52 – 850 kW wind turbine. Typical noise at 10 m/s wind speed ...... 78 Figure 40: Low frequency sound from DAT tape ‐ Bonus 1. 3 MW wind turbine to 200 Hz 78 Figure 41: The relationship between the background noise levels and recommended noise limits set out in NZS6808:2010...... 82 Figure 42: ‘Current’ wind farms development in New Zealand ...... 88 Figure 43: Sample of wind turbine rotor diameter size versus time [1985 to 2007] ...... 89 Figure 44: Sample of wind turbine rotor diameter versus sound power level ...... 89 Figure 45: Basic components of a wind turbine rotor blade and aerofoil cross section...... 95 Figure 46: Basic components of a wind turbine rotor and blades [3d]...... 95 Figure 47: V72/NM72 wind turbine rotor and blades at Te Apiti Wind Farm...... 95 Figure 48: Site location map for Te Apiti and West Wind [Makara] Wind Farms, Lower North Island, New Zealand...... 100 Figure 49: 2D contour map of Project West Wind [Makara] Wind Farm, 403 Makara Road and D12 Wind Turbine Generator...... 101 Figure 50: 2D aerial photo of Project West Wind [Makara] Wind Farm, showing 403 Makara Road and closest wind turbine generators with access tracks. Drawing adapted from Google Earth to include turbines...... 102 Figure 51: Black and white 2d aerial photo with Te Apiti Wind Farm, including Tap 44 wind turbine generator and tracks...... 103 Figure 52: 3D aerial representation with Te Apiti Wind Farm overlay, including Tap 44 wind turbine generator & Ro measurement location. Note undulating terrain. Drawing adapted from Google Earth to include turbines...... 103

Figure 53: Illustration of the definitions of Ro and slant distance R1 [...... 104 Figure 54: 2d base aerial photo with Te Apiti Wind Farm Tap 44 wind turbine generator

[protruding 3d] and Ro measurement location...... 105

Figure 55: 3d aerial photo with Te Apiti Wind Farm Tap 44 wind turbine generator and Ro measurement location...... 105

xvi

Figure 56: 3D schematic of 403 Makara Road location relevant to D12 wind turbine generator. Note steep surrounding terrain and hills. Drawing adapted from Google Earth to include 403 Makara Road and D12...... 107 Figure 57: 3D aerial photo of Project West Wind [Makara] Wind Farm, showing 403 Makara Road and closest wind turbine generators with access tracks. Drawing adapted from Google Earth to include 403 Makara Road and D12 ...... 108 Figure 58: Visualization of D12 wind turbine blades as viewed from 403 Makara Road ...... 108 Figure 59: Te Apiti Wind farm as viewed from off the wind farm site, looking east‐ward towards farm...... 109 Figure 60: Photo simulation as viewed from base of Tap 44 360 degree view...... 109 Figure 61: Photo viewed from base of Tap 44 looking approx north‐west towards turbine Tap 26 in foreground...... 109 Figure 62: Photo viewed from base of Tap 44 looking approx north towards turbine Tap 45 in foreground...... 110 Figure 63: Photo viewed from base of Tap 44 looking approx south. Note fence line represents wind farm site boundary with steep drop off terrain towards below...... 110 Figure 64: Photo viewed from base of Tap 44 looking approx west, turbines in far background from Tauraua Wind Farm [along ridge line]...... 111 Figure 65: Photo viewed from approx north‐west looking towards base of Tap 44...... 111 Figure 66: Photo viewed from approx south west looking towards base of Tap 44. Tap 45 in foreground...... 112 Figure 67: Photo viewed from approx south east looking towards base of Tap 44. Tap 26 in foreground...... 112 Figure 68: Photo viewed from aircraft of West Wind, Wind Farm...... 113 Figure 69: Technical drawing of front and side elevations of Vestas V72 Wind Turbine Generator including key dimensions and photo...... 115 Figure 70: Technical drawing of front and side elevations of Siemens SWT 2.3‐82V Wind Turbine Generator including key dimensions and photo...... 115 Figure 71: Graph of Sound Power Level for Vestas V72 wind turbine generator at various frequencies [standard and setting 4 sound powers operating modes provided]...... 118 Figure 72: Graph of Measured Sound Power Level for Vestas V72 wind turbine generator at various frequencies for 8 m/s operating speed [standard sound power operating mode provided]...... 119 Figure 73: 2260 Bruel and Kjaer Integrating Sound Level Meter and calibrator and wind screens...... 120 Figure 74: M‐Audio Micro Track II and related equipment used in study...... 120 Figure 75: Garmin GPS Unit...... 121 Figure 76: Garmin GPS Unit at base of Tap 44, Te Apiti Wind Farm...... 121 Figure 77: Garmin GPS Unit Software and tracking GPS points ...... 122

xvii

Figure 78: Heavy duty pelican case used in study for weather protection of measurement apparatus ...... 123 Figure 79: 2D map with Te Apiti Wind Farm and wider surrounding environment [including existing and proposed wind farm developments...... 126 Figure 80: 3D colour schematic of 403 Makara Road location relevant to D12 wind turbine generator...... 128 Figure 81: NIWA median annual average wind speed map for New Zealand...... 130 Figure 82: Sample Wind Rose for Makara area – All wind directions ...... 131 Figure 83: Sample wind rose for Makara area – All wind directions ...... 132 Figure 84: Sample wind rose for Makara area – [Left] Night time [Right] Day time wind directions ...... 132 Figure 85: Sample wind rose for Te Apiti – All wind directions ...... 133 Figure 86: Schematic flow diagram of set up for field measurement testing of sound pressure levels and audio recording...... 137 Figure 87: Schematic flow diagram of set up for field measurement testing of sound pressure levels...... 140 Figure 88: Graph of measured sound pressure levels with equipment failure of microphone versus time...... 143 Figure 89: Graphic of rain radar from New Zealand Met Service...... 145 Figure 90: Graphic of weather data for 24 hour period from weatherunderground.com ...... 145 Figure 91: Graph of filters applied to measured sound pressure levels and number of raw samples ...... 148 Figure 92: Scatter graph with second order polynomial curve of measured 10 minute sound

pressure levels versus measured wind speed at V10m and V Hub Height...... 152 Figure 93: Graph of expected wind farm sound pressure levels only versus actual measured wind farm and wind farm plus background sound pressure levels ...... 153 Figure 94: Graph of fundamental relationship between wind speed levels at V=10 m and Beaufort Scale Number [Land scale] ...... 155 Figure 95: Graph of measured wind turbine & background sounds versus time, levels

presented as LAeq...... 158 Figure 96: Schematic of a low signal to noise ratio illustrating an obtrusively high background noise level masking a desired sound signal from the wind turbine sounds...... 163 Figure 97: Schematic of a preferred signal to noise ratio illustrating a high signal from the wind turbine above masking signals from background noise levels...... 163 Figure 98: Flow chart of method...... 165 2 Figure 99: Graph of R values LAeq versus LA90. 403 Makara Road, 10 minutes Sampling Time, Data Sets B to N ...... 170 2 Figure 100: Graph of R values LAeq / LA90 versus wind speed [V=Hub height]...... 170

Figure 101: Graph of actual measured time varying sound pressure level of LA90 vs wind speed and expected wind farm sound level only ...... 171

xviii

Figure 102: Graph of actual measured time varying sound pressure level of LAeq vs wind speed and expected wind farm sound level only [expressed as best fit line [log function]. .. 172 Figure 103: Graph of calculated expected wind farm sound pressure level only expressed as

LAeq and LA90 vs wind speed 403 Makara Road...... 173 Figure 104: Graph of calculated expected wind farm sound pressure level only expressed as

LAeq and LA90 vs wind speed 403 Makara Road ...... 173 Figure 105: Graph of calculated expected wind farm sound pressure level only expressed

as LAeq and LA90 vs wind speed 403 Makara Road ...... 174

Figure 106: Graph of historic measured time varying sound pressure level of LAeq and LA90. Date of sample 23 June 1997 to 14 August 1997 [22 days]...... 175 Figure 107: Graphic of mean level sound level differences for 403 Makara Road and Te Apiti Wind Farm...... 186

Figure 108: Example of a direct positive relationship between LAeq or LA90 sound descriptors where the arrows represent an increase or decrease in sound levels...... 193

Figure 109: Example of a direct negative relationship between LAeq or LA90 sound descriptors where the arrows represent an increase or decrease in sound levels...... 193 Figure 111: Scatter graph of rank [Data Set M] Spearman Rank Correlation Coefficient...... 200 Figure 112: Scatter graph of rank [Data Set N] Spearman Rank Correlation Coefficient...... 200

Figure 113: Scatter graph of LA90 versus LAeq for Data Set B...... 204

Figure 114: Scatter graph of LA90 versus LAeq for Data Set M...... 204

Figure 115: Scatter graph of LA90 versus LAeq for Data Set N...... 205

Figure 116: Scatter graph of LAeq [redline, with red dots] and LA90 [blue line with blue dots] versus wind speed at hub height [m/s] for Data Set B ...... 205

Figure 117: Scatter graph of LAeq [redline, with red dots] and LA90 [black line with blue dots] versus wind speed at hub height [m/s] for Data Set M ...... 206

Figure 118: Scatter graph of LAeq [redline, with red dots] and LA90 [black line with blue dots] versus wind speed at hub height [m/s] for Data Set N...... 206 Figure 119: [Top] 2d [Bottom] 3d ‐ Prediction of sound pressure level for 403 Makara Road

Contours of equal sound pressure levels between LAeq 35 and 50 dB...... 208 Figure 120: Graph of measured instantaneous time varying sound pressure level for 30

second measurement period with the same LAeq sound level ...... 210 Figure 121: Graph of measured instantaneous time varying sound pressure level and noise descriptor relationships...... 211 Figure 122: Graph of measured instantaneous time varying sound pressure level from

non-filtered raw data [LAeq and LA90] at 403 Makara Road...... 212

Figure 123: Time varying graph LA95 dB Sample A...... 213

Figure 124: Time varying graph LA95 dB Sample B...... 213

Figure 125: Time varying graph LA95 dB Sample C...... 214

Figure 126: Time varying graph LA95 dB Sample D...... 214

Figure 127: Time varying graph LA95 Sample E...... 215

xix

Figure 128: Percentile levels...... 218 Figure 129: Sound level distribution curves...... 219 Figure 130: Example of noise floor in study measurements...... 222 Figure 131: Bruel and Kjaer Pulse System ...... 224

xx

List of Tables Table 1: Noise annoyance moderators ...... 27 Table 2: Aero acoustic mechanisms of a wind turbine generator ...... 53 Table 3: Frequency ranges covered and method of exposure from seven studies...... 67

Table 4: Comparison of dBA and dBLin values in several low Frequency environments...... 74 Table 5: Relationship between the background noise levels and recommended noise limits set out in NZS6808:2010...... 83 Table 6: Wind farm noise limits set in other countries ...... 84 Table 7: Te Apiti Wind Farm, Tap 44 Wind Turbine Generator New Zealand Map Grid Northing Northing & Easting coodinates, Ro assessment location heights & distances...... 106 Table 8: Project West Wind, Wind Farm, D12 Wind Turbine Generator & 40 Makra Road New Zealand Map Grid Northing and Easting co‐ordinates, heights and distances. ... 107 Table 9: Table of generic specifications for test turbines ‐ Vestas V72 and Siemens SWT 2.3-82V wind turbine generator ...... 114 Table 10: Measured Apparent Sound Power Level for Vestas V72 Wind Turbine Generator. . 117 Table 11: Measured Apparent Sound Power Level for Siemens SWT 2.3‐82V ...... 117 Table 12: Measured Apparent Sound Power Level for Vestas V72 ...... 117 Table 13: Measured Apparent Sound Power Level for Vestas V72...... 118 Table 14: Description of key sound level measuring apparatus used in study...... 119 Table 15: Description of audio level measuring apparatus used in study...... 120 Table 16: Description of key handheld weather apparatus used in Study...... 121 Table 17: Description of GPS apparatus used in study...... 121 Table 18: Description of various supplementary apparatus used in study...... 123 Table 19: Description of filters applied to measured sound pressure levels and number of raw samples...... 147

Table 20: Statistical table of measured time varying sound pressure level of LAeq and LA90. 403 Makara Road. 10 minutes Sampling Time. Data Set M...... 166

Table 21: Statistical table of measured time varying sound pressure level of LAeq and LA90. 403 Makara Road. 10 minutes Sampling Time. Data Set N ...... 166

Table 22: Statistical table of measured time varying sound pressure level of LAeq and LA90 at wind speeds 4 to 10 m/s. 403 Makara Road...... 167

Table 23: Summary statistical table of measured time varying sound pressure level of LAeq

and LA90. 403 Makara Road. 10 minutes Sampling Time. Data Sets B to L ...... 169 2 Table 24: Summary statistical table of R values LAeq versus LA90 versus wind speed [V=Hub height] 403 Makara Road. 10 minutes Sampling Time. Data Sets B to N ...... 169

Table 25: Summary table of actual measured time varying sound pressure level of LA90 vs wind speed and expected wind farm sound level only [expressed as best fit line [log function]. 403 Makara Road...... 171

xxi

Table 26: Summary table of actual measured time varying sound pressure level of LAeq vs wind speed & expected wind farm sound level only [expressed as best fit line ...... 172 Table 27: Summary table of calculated expected wind farm sound pressure level only

expressed as LAeq and LA90 vs wind speed 403 Makara Road ...... 174

Table 28: Statistical table of measured time varying sound pressure level of LAeq and LA90. 403 Makara Road. 10 minutes sampling time. Data Set N ...... 185

Table 29: Statistical table of measured time varying sound pressure level of LAeq and LA90.

Te Apiti Wind Farm Tap 44 – Ro measurement location and base of wind turbine generator. Sampling time as shown...... 185 Table 30: Calculated Spearman Rank Correlation Coefficient [SRCC] and Kendall tau Rank Correlation Coefficient [KRCC] for all data [Data Set B], Data Set M & Data Set N .... 199 Table 31: Examples from IEC 61400‐11: Wind Turbine Generator Systems Part 11: Acoustic Noise Measurement Techniques of possible values of uncertainty components relevant for apparent sound power level measurements ...... 220 Table 32: Inherent noise level of 2260 Bruel and Kjaer Sound Level Meter ...... 221

xxii